Function iflib_netmap_txsync

freebsd/net/iflib.c:959–1113

* Reconcile kernel and user view of the transmit ring. * * All information is in the kring. * Userspace wants to send packets up to the one before kring->rhead, * kernel knows kring->nr_hwcur is the first unsent packet. * * Here we push packets out (as many as possible), and possibly * reclaim buffers from previously completed transmission. * * The caller (netmap) guarantees that there is

 * methods should be handled by the individual drivers.
 */
static int
iflib_netmap_txsync(struct netmap_kring *kring, int flags)
{
	struct netmap_adapter *na = kring->na;
	if_t ifp = na->ifp;
	struct netmap_ring *ring = kring->ring;
	u_int nm_i;	/* index into the netmap kring */
	u_int nic_i;	/* index into the NIC ring */
	u_int n;
	u_int const lim = kring->nkr_num_slots - 1;
	u_int const head = kring->rhead;
	struct if_pkt_info pi;

	/*
	 * interrupts on every tx packet are expensive so request
	 * them every half ring, or where NS_REPORT is set
	 */
	u_int report_frequency = kring->nkr_num_slots >> 1;
	/* device-specific */
	if_ctx_t ctx = ifp->if_softc;
	iflib_txq_t txq = &ctx->ifc_txqs[kring->ring_id];

	bus_dmamap_sync(txq->ift_ifdi->idi_tag, txq->ift_ifdi->idi_map,
	    BUS_DMASYNC_POSTREAD | BUS_DMASYNC_POSTWRITE);

	/*
	 * First part: process new packets to send.
	 * nm_i is the current index in the netmap kring,
	 * nic_i is the corresponding index in the NIC ring.
	 *
	 * If we have packets to send (nm_i != head)
	 * iterate over the netmap ring, fetch length and update
	 * the corresponding slot in the NIC ring. Some drivers also
	 * need to update the buffer's physical address in the NIC slot
	 * even NS_BUF_CHANGED is not set (PNMB computes the addresses).
	 *
	 * The netmap_reload_map() calls is especially expensive,
	 * even when (as in this case) the tag is 0, so do only
	 * when the buffer has actually changed.
	 *
	 * If possible do not set the report/intr bit on all slots,
	 * but only a few times per ring or when NS_REPORT is set.
	 *
	 * Finally, on 10G and faster drivers, it might be useful
	 * to prefetch the next slot and txr entry.
	 */

	nm_i = kring->nr_hwcur;
	if (nm_i != head) {	/* we have new packets to send */
		uint32_t pkt_len = 0, seg_idx = 0;
		int nic_i_start = -1, flags = 0;
		pkt_info_zero(&pi);
		pi.ipi_segs = txq->ift_segs;
		pi.ipi_qsidx = kring->ring_id;
		nic_i = netmap_idx_k2n(kring, nm_i);

		__builtin_prefetch(&ring->slot[nm_i]);
		__builtin_prefetch(&txq->ift_sds.ifsd_m[nic_i]);